Have Lots Of Confusion On My Batteries and Voltage

Some history/background info to start. The trailer is new to me and so is full timing. It's 41' race trailer with living quarters in the front. I have a bank of batteries that is run through and inverter and that bank consists of 4 Trojan 6V batteries in series and parallel for a total of 480 amps. I also have a bank of 4 Duralast batteries that are 12V and in parallel for a total of 340 amps. The batteries are all new within a week.

Right now I'm trying to figure out issues with the 12v bank (Duralast). I have a diesel heater (12V) that I am trying to run which at max is 7 amps (that's full bore and does not constantly run at that rate). From the calculators I found online I should be able to run the heater for 31 hours straight (at that 7 amps) before hitting 50% charge.... Well what I'm finding is when I turn on lights and run the heater my batteries are at 12.27V with a voltmeter reading across the terminals. I'm a bit perplexed and exhausted of reading articles about batteries. I'm not quite finding the answer to my issue. The store clerk I bought the Trojans from said he can run 4 straight days in a small travel trailer without having to recharge his Trojans (same setup).

I was expecting better performance from all of this and feel like I have quite a solid battery setup. I've read articles of people who say they can run their microwave (or should be able to) for 2 solid hours with the same battery setup as myself. Why are my batteries dropping so quickly (within an hour). They are hooked to 4 solar panels that are 145W each and had a full charge before this last experiment.

Any help and advice is greatly appreciated. I'm about ready to pull my hair out over this because I've had battery issues in the past truck camper I had. I spent many nights in Alaska completely frozen because of a dead battery and not understanding that it's dead at 12.1-12.2 volts. I went with a large battery setup so I can boondock and still be warm at night while also being able to turn lights on. Thank you

21 Replies

pianotuna
Nomad III
Mar 09, 2014
Hi,

Do you have a way to switch or combine between banks?

Very few folks have two battery banks. Even fewer have both six and twelve volt jars.

It is possible to have switches to allow both banks to be drawn on at once, as well as sharing charging. Or using one bank while charging the other.

Trojan wants voltages as high as 15.8 volts (for a series paring of six volts) to completely charge their products. The existing controller must be capable of allowing charging set point changes and be adjusted to that number. If not, it will force you to use shore or generator power at least once per week to fully charge them.

I have two banks--but my batteries are all identical makes. They are different ages, which is one reason I chose to separate them.

How large (watts) and what make and model is the inverter?
pianotuna
Nomad III
Mar 09, 2014
Hi,

How long did you charge the batteries i.e. how many hours (on shore power)?

The wires from the buss to each of the batteries must be equal lengths. If not the batteries can never be equally charged nor fully charged.

If you wish to understand the "why" surf here:

correctly interconnecting multiple twelve volt batteries

Others may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?
tlukasavige172
Explorer
Mar 09, 2014
I have 2 separate charge controllers. The 20L is running off 2 145W panels and I can't remember the name of the other although it is larger and it's running to the bank of 4 6V Trojan batteries. I had an RV solar store install the package and they did it so I could add batteries to the system. I'm questioning their intelligence though as I'm learning more and more about this.
EsoxLucius
Explorer
Mar 09, 2014
580 watts of solar on a single 20 amp charge controller? How does that work?
tlukasavige172
Explorer
Mar 09, 2014
Both banks of batteries are charged off solar panels.

When I added the 2 extra batteries to the 12V bank (the Duralast 12V batteries) the original 2 were 6 months old.

The solar consists of 4 145W panels.

I have 4 12V batteries at 85W a piece (these are the Duralast)

I started with a full charge.

How do you wire batteries in a balanced manner? Can you explain that?
wa8yxm
Explorer III
Mar 09, 2014
7*31 = 217 amp hours times two = 432 amnp hours.. That's a lot of 12 volt batteries.

First you have several issues you did not address.
How many 12 volt batteries do you have (Looks like 4 Group 29's to me) what size are they, How long since you cleaned the connections, many connections, what converter do you have, did you start with a full charge.

You might find that GC-2 pairs (two six volt batteries connected in series to make one BIG (230 amp hour) battery in series) work better (Well 3 of them would be 460 amp hours at the c/20 rate. or not, they would likely be less expensive (<90 each at Sam's). Or not.

Also, be warned.. Some battery makers use different formulas for calcing the amp hour capacity.. Wal*mart for example uses the 1 amp rate.. so if it says 100 amp hours, it means it can put out one amp for 100 hours.

But we use the c/20 rate, so that same battery is like 70 amp hours at teh c/20 rate.
badboy368
Explorer
Mar 09, 2014
another thing to consider is to make sure not only that there is no draw on the batteries, is to make sure your charger is completely off/disconnected. if it is putting any power to the battery, that is what the reading you will get. please don't ask how i learned that :S
pianotuna
Nomad III
Mar 09, 2014
Hi,

Mixing new batteries with old doesn't work well. The bank with the 12 volt jars probably has only 3/4 the amp-hours you think it does, especially if not wired in a balanced manner.

How many watts is the solar system?

How is the bank of trojans charged?

Please answer the rest of the questions?
tlukasavige172
Explorer
Mar 09, 2014
Okay thank for clearing that up. That seems like a much simpler way of looking at it then I've seen.

One bank is for the 12V system and the other runs to the inverter.
AH64ID
Explorer
Mar 09, 2014
Why does the trailer have 2 banks?

340ah divided by two gives you 170ah until 50% charge. So with 170ah available, and drawing 7a for the furnace you get 24 hours.

The furnace will draw a constant amount if watts, as voltage drops amperage increases. So if a furnace draws 7 amps at 12.5v it would draw 7.4 amps at 11.8v.